The present invention relates to installations for treating at least one fluid, of the type comprising, in a container, at least one mass of particulate material which is retained between two perforated walls and through which the fluid flows in an approximately horizontal direction, and, near the upper part of the mass, at least one deflecting surface extending from a first of said walls toward the second wall, making an angle with the horizontal flow direction of the fluid.
An installation of this type is disclosed in document FR-A-2 741 823. In the installations disclosed in that document, the volume around the open region for charging with particulate material at the end of the deflecting surface is entirely occupied by the particulate material.